The invention relates to a method of embedding a watermark in an image, comprising the steps of calculating a saliency of image pixels, identifying salient image pixels, and processing the image in such a way that a predetermined percentage of the most salient image pixels lies within the vicinity of a predetermined watermark pattern. The invention also relates to an arrangement for embedding a watermark in an image.
A known method of embedding a watermark as defined in the opening paragraph is disclosed in M. J. J. B. Maes and C. W. A. M. van Overveld: xe2x80x9cDigital Watermarking by Geometric Warpingxe2x80x9d, Proceedings of the 1998 International Conference on Image Processing, Oct. 4-7, 1998, pages 424-426. In this known method, the watermark is a predetermined image pattern, for example, a pattern of lines. The image is watermarked if a statistically high percentage of salient pixels of the image lies within the vicinity of the watermark pattern. This is achieved by identifying the salient pixels, and moving (xe2x80x9cwarpingxe2x80x9d) them to the vicinity of the watermark pattern. The step of image processing thus comprises locally changing the geometrical characteristics of the image.
It is an object of the invention to embed the watermark using an alternative method of image processing.
To this end, the method in accordance with the invention is characterized in that the step of processing the image comprises modifying the saliency of salient pixels. The watermark is thus embedded by modifying the saliency of image pixels instead of moving them to different positions. The saliency is modified by decreasing the saliency of most salient pixels not lying within the vicinity of the watermark pattern and/or increasing the saliency of salient pixels lying within the vicinity of the watermark pattern. Advantageous embodiments of identifying and modifying salient pixels are defined in the dependent claims.